Several techniques and systems have been developed for use in correcting and stabilizing spinal curvatures, and for facilitating spinal fusion in the case of spinal disorders or degenerative conditions. Typically, a pair of bendable rods are longitudinally disposed adjacent the vertebral column and are fixed to various vertebrae along the length of the spine by way of a number of fixation elements, such as hooks and screws.
Numerous spinal rod systems have been developed which provide transverse connectors for linking the adjacent spinal rods across the spinal midline to provide a rigid and stable construct. Most of these systems present one or more difficulties for spinal surgeons. Many of the devices are high profile which increases soft tissue trauma and surgical complications. Furthermore, in many of these prior systems the attachment mechanisms must be preloaded on the spinal rods which can require significant pre-operative planning and which virtually eliminates the opportunity to add connectors in situ.
One transverse connector system is the TSRH.RTM. CROSSLINK.RTM. of Danek Medical, Inc. The TSRH.RTM. CROSSLINK.RTM. utilizes a three point shear clamp mechanism which restricts motion between the rods in all directions, and particularly resists axial forces between rods and torsional moments about the axis of the rods. A quadrilateral construct is formed by laterally connecting the rods across the sagittal plane with rigid plates. The lateral connection reduces the loss of correction that can occur over time.
Rigid transverse connections between spinal rods are beneficial because they restrict rod migration and increase construct stiffness. In many cases involving multi-level fusion of the spine, these features are essential while solid bone fusion is accomplished. In the post-operative period before fusion occurs, a significant amount of motion can occur between the rods, wires and hooks, which can, for example, allow a scoliotic correlation to decrease or the pelvis to de-rotate toward its previous, deformed position. By providing a rigid transverse connection between two spinal rods, the loss of correction can be reduced and a stiffer construct can be created which may enhance the promotion of a solid fusion. While the TSRH.RTM. CROSSLINK.RTM. provides an excellent construct, a need has remained for low profile devices which link adjacent spinal rods in a top-loading and top-tightening fashion with a minimum of components and steps.